Method of producing vanadium compounds by alkaline leaching

ABSTRACT

VANADIUM COMPOUNDS ARE PRODUCED FROM ORES BY ADDING SODIUM HYDROXIDE OF POTASSIUM HYDROXIDE TO FINELY GROUND RAW MATERIAL WHICH CONTAINS V2O3 OR ANOTHER INSOLUBLE FROM OF VANADIUM, THE CONCENTRATION OF THE SODIUM HYDROXDE OR POTASSIUM HYDROXIDE BEING IN THE RANGE OF 250 TO 400 G./L. NA2O OR K2O, WHEREIN THE REACTION MIXTURE IS HEATED TO A TEMPERATURE OF AT LEAST 250* AND OXYGEN OR COMPRESSED AIR ADDED TO OXIDIZE THE V2O3 TO V2O5, AND THEN FILTERING THE SOLUTION SO AS TO SEPARATE THE CRYSTALLINE ALKALINE VANADATE FORMED. IN ADDITION, PRIOR TO THE CRYSTALLIZATION SLUBLE FLUORIDES OR PHOSPHATES MAY BE ADDED TO THE SOLUTION SO AS TO FURTHER INCREASE THE CRYSTALLIZATION.

United States Patent 3 712 942 METHOD OF PRODiJCIlVG VANADIUM COM-POUNDS BY ALKALINE LEACHING US. Cl. 423-593 Claims ABSTRACT OF THEDISCLOSURE Vanadium compounds are produced from ores by adding sodiumhydroxide or potassium hydroxide to finely ground raw material whichcontains V 0 or another insoluble form of vanadium, the concentration ofthe sodium hydroxide or potassium hydroxide being in the range of 250 to400 g./l. Na O or K 0, wherein the reaction mixture is heated to atemperature of at least 250 and oxygen or compressed air is added tooxidize the V 0 to V 0 and then filtering the solution so as to separatethe crystalline alkaline vanadate formed. In addition, prior to thecrystallization soluble fluorides or phosphates may be added to thesolution so as to further increase the crystallization.

This invention relates to a method of producing vanadium compounds byalkaline leaching.

According to known methods of operation, vanadium compounds,particularly V 0 are produced from ores by calcination with oxidation ofthe raw material by the addition of *NaOl, NaiSO, and the like, in asuitable furnace utilizing a temperature of about 1000 C. The rawmaterial consists of ores or of so-called vanadium slag which containstrivalent vanadium in insoluble form, mostly bound to oxides of the typeR0 in spinel-bond. Since this bond is very stable, its decompositionrequires the application of a very high temperature during the heatingstep. In addition, the oxidation reaction, in solid or semi-liquid form,of this charge with its heterogeneous character, takes a slow course,the vanadium yield amounting to more than 70-80% and the escaping gascontaining harmful substances, particularly C1 and HCl. Furtherdisadvantages are the low thermal efficiency of the furnace, theproduction of diluted vanadate solutions and the insuflicient purity ofthe obtained V 0 since only 90-95% is recovered at the firstprecipitation, thereby requiring an additional refinement whichcomplicates the process.

The present invention is an improvement over these prior known methodsand eliminates the drawbacks therein. According to the presentinvention, finely ground raw material which contains V 0 or some otherinsoluble form of vanadium is utilized and a solution of sodiumhydroxide or potassium hydroxide is added to it in a concentration of250-400 g. per liter of Na O or K 0. Utilizing a pressure pump theobtained reduction mixture is pumped into a through-flow autoclave whereit is heated to a temperature of at least 250, preferably to 320-340 C.At the same time, gaseous oxygen or air is passed into the solution, ahigher pressure being utilized with air due to its smaller oxygencontent. A pressure of 120-180 kp./cm. is required according to thetemperature used and to the resistance of the autoclave. An oxidation ofthe insoluble V 0 to V 0 takes place. The V 0 is soluble in the solutionand enters the solution in the form of Na V0 The solution is then cooledto a temperature of below 30 C., preferably to 5-10 C. with theaccompanying separation of pure crystalline 3,712,942 Patented Jan. 23,1973 Na VO.,- 8-12H O. Only about 1 to 2 g./l. of V 0 remain in themother liquor. This percentage can be further re duced by the additionof fluorine salts or phosphates such as NaF, Na PO or the like.Continued crystallization reduces the V 0 content in the mother liquorto 0.5 to l g./l. A1 0 and the like is dissolved during the leachingaction. Prior to crystallization, these substances can be precipitatedby lime and filtered out. By crystallizing out the vanadates, andthereafter thickening the liquor, it can again be used for the treatmentof raw materials. From the Na VO obtained, V 0 can be produced in theusual way by acidifying the salt after dissolving it in water, filteringout the vanadium acid and remelting the substance.

Thus, the present invention relates to a method of obtaining vanadiumcompounds by adding sodium hydroxide or potassium hydroxide to finelyground raw material which contains V 0 or some other insoluble form ofvanadium, the concentration of the NaOH or KOH being 250 to 400 g./l. NaO or K 0, preferably 320 to 350 g./l., by heating the reaction mixtureto a temperature of at least 250 C., preferably 320-340 C., and thenoxidizing with oxygen or compressed air and thereupon filtering thesolution and cooling it down to a temperature below 30 C., preferably5-l0 C., so as to separate the crystalline alkaline vanadate. The V 0content in the mother solution is further reduced by the addition ofsoluble fluorides or phosphates bywhich the crystallization effect isincreased.

Example 1 One ton of vanadium slag is used. After the elimination ofiron, the vanadium slag is mixed with the addition of 8 to m. of asolution which contains 300-350 g./l. of Na O (in the form of NaOH).Using a pressure of kp./cm. the reaction mixture is transferred into atube-autoclave fitted with a heat exchanger where it is progressivelyheated to 340 C. Simultaneously, an excess quantity of compressed oxygenis. driven in, the oxygen together with any air therein being laterseparated using a tower-type separator. After the heating step andcooling it down to about 100 C., the solid residue is filtered out andwashed by means of vacuum filters. The solution containing 10-20 g./l. V0 20-30 g./l. SiO and 10 g./l. A1 0 is precipitated, in a mixer, byfresh lime. The calcium silicate and calcium aluminate obtained isfiltered out and Washed. These can be secondary products. In athrough-flow crystallizer, the residual solution is cooled down to 10 C.whereby crystalline is separated. After the filtration of this product,vanadium salts or V 0 are produced in the usual manner.

The mother solution, having a content of 1 g./l. V 0 is evaporated to aconcentration of 550-600 g./l. Na O. By further cooling it down to l0-20C., the remaining impurities are eliminated and filtered. The mothersolution may also be cooled down to 10 C., without preliminaryevaporation. In this way the impurities are also separated. Then, themother solution can again be used for the preparation of the charge.

It will be obvious to those skilled in the art that various changes maybe made without departing from the scope of the invention and theinvention is not to be considered limited to what is described in thespecification.

What is claimed is:

1. A method of producing vanadium compounds from finely ground rawmaterial which contains V 0 or some other insoluble form of vanadiumwhich comprises adding NaOH or KOH being 250-400 g./l. Na O or K 0,heating the reaction mixture to a temperature of between about 320340C., supplying oxygen or compressed air at a pressure exceeding 120atmospheres and oxidizing said reaction mixture solution, filtering thesolution, cooling the resultant to a temperature below 30 C., adding asodium fluoride to said cooled solution and precipitating a crystallinealkaline vanadate, and finally filtering out the precipitate.

2'. A method in accordance with claim 1 wherein the concentration ofNaOH or KOH is between 320-350 g./l.

3. A method in accordance with claim 1 wherein the reaction mixture isheated to a temperature of 320 340 C.

4. A process in accordance with claim 1 wherein the solution is cooledto a temperature of 5l0 C.

5. A method in accordance with claim 1 wherein the concentration of NaOHor KOH is 320350 g./l., the reaction mixture is heated to a temperatureof 320- 340 Cfand the solution is cooled to a temperature of 510 C.

References Cited UNITED STATES PATENTS MILTON WEISSMAN, Primary Examiner11.5. C1. X.R.

